1. Field of the Invention
This invention relates to a method and apparatus for preheating and charging scrap metal for steel making in a converter or the like. More particularly, a heating installation is provided for scrap preheating and an elongated, transportable trough is designed for the charging of the preheated scrap into the converter.
2. Description of the Prior Art
Prior art apparatus and methods are described in the publication "Prospects for Scrap Preheating for the Basic Oxygen Furnace," Steel Times, Sept. 1972, pp. 679-682. According to this publication, scrap is heated in standard charging troughs, then charged into a converter. As is well known, in this type of scrap preheating outside the converter, the main unit proper, i.e., the converter, is unloaded. Scrap that has been heated to 500.degree. to 600.degree. and possibly even 800.degree. C. or more, can be charged into the converter at any time during a converter cycle, e.g., prior to or after the addition of pig iron. Compared to adding non-preheated scrap for cooling directly into the converter, the tap-to-tap time of the converter is shorter and the disadvantages encountered in the prior art when adding scrap to the converter are non-existent. A particular advantage of the charging of preheated scrap is that at 700.degree. C. and above, scrap exhibits a certain softness so that it requires less space compared to non-preheated scrap.
In a prior art process for scrap preheating in a charging trough, scrap is first fed into the charging trough, whereupon a hood-like cover provided with heaters is applied to the filled charging trough. The heaters, typically oil burners, are used to heat the scrap. Upon removal of the hood, the charging trough can be transported to the converter and emptied therein. This method and the equipment operating according thereto have the disadvantage that the charging trough is heated at the same time as the scrap. This results in an enormous energy loss, since the mass of the charging trough is somewhat comparable with the mass of the scrap charged into it. Roughly speaking, the charging trough absorbs about 50% of the heat supplied, but the heat absorbed by the charging trough is lost for subsequent steel production. There is also the danger that the charging trough will distort and scale.
Although preheating scrap directly within the charging trough has advantages as far as the transport of scrap is concerned, such preheating has drawbacks with respect to the associated energy consumption and the wear of the charging troughs. Yet another disadvantage of such a prior art process is the potential for oxidation of the scrap from direct contact with the heating flame.